Android. Откройте список контактов устройства, если он не работает. Невозможно создать экземпляр активности. ComponentInfo

Question

Это эксперимент для понимания того, что может предложить ContactsContract. Я не знаю, что я сделал неправильно ... Пожалуйста, помогите мне с этой проблемой. Мой код:

package com.example.beni.contactbrowser1; 

import android.content.Intent; 
import android.net.Uri; 
import android.os.Bundle; 
import android.provider.ContactsContract; 
import android.support.v7.app.AppCompatActivity; 
import android.support.v7.widget.Toolbar; 
import android.view.View; 
import android.view.Menu; 
import android.view.MenuItem; 
import android.widget.Button; 
import android.widget.TextView; 

public class MainActivity extends AppCompatActivity { 
    static final int PICK_CONTACT_REQUEST = 1; 
    TextView tv = (TextView) findViewById(R.id.textView); 

    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_main); 
     Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar); 
     setSupportActionBar(toolbar); 

     Button button= (Button) findViewById(R.id.b1); 
     button.setOnClickListener(new View.OnClickListener() { 
      @Override 
      public void onClick(View v) { 
       //DoIt(v); 
       //alarm.setAlarm(MainActivity.this); 
       pickContact(); 
      } 
     }); 
    } 

    @Override 
    public boolean onCreateOptionsMenu(Menu menu) { 
     // Inflate the menu; this adds items to the action bar if it is present. 
     getMenuInflater().inflate(R.menu.menu_main, menu); 
     return true; 
    } 

    @Override 
    public boolean onOptionsItemSelected(MenuItem item) { 
     // Handle action bar item clicks here. The action bar will 
     // automatically handle clicks on the Home/Up button, so long 
     // as you specify a parent activity in AndroidManifest.xml. 
     int id = item.getItemId(); 

     //noinspection SimplifiableIfStatement 
     if (id == R.id.action_settings) { 
      return true; 
     } 

     return super.onOptionsItemSelected(item); 
    } 

    @Override 
    public void onActivityResult(int requestCode, int resultCode, Intent intent){ 
     super.onActivityResult(requestCode, resultCode, intent); 
     if (requestCode == PICK_CONTACT_REQUEST) { 

      if (resultCode == RESULT_OK) { 
       Uri pickedPhoneNumber = intent.getData(); 
       // handle the picked phone number in here. 
       tv.setText(pickedPhoneNumber.toString()); 
      } 
     } 
    } 

    private void pickContact() { 
     Intent pickContactIntent = new Intent(Intent.ACTION_PICK, ContactsContract.Contacts.CONTENT_URI); 
     pickContactIntent.setType(ContactsContract.CommonDataKinds.Phone.CONTENT_TYPE); 
     startActivityForResult(pickContactIntent, PICK_CONTACT_REQUEST); 
    } 
} 

Эти журналы ошибок появляется, когда я запустить приложение приложения:

01-15 12:59:09.004 7447-7447/com.example.beni.contactbrowser1 D/AndroidRuntime: Shutting down VM 
01-15 12:59:09.004 7447-7447/com.example.beni.contactbrowser1 W/dalvikvm: threadid=1: thread exiting with uncaught exception (group=0x4001e6a8) 
01-15 12:59:09.007 7447-7447/com.example.beni.contactbrowser1 E/AndroidRuntime: FATAL EXCEPTION: main 
01-15 12:59:09.007 7447-7447/com.example.beni.contactbrowser1 E/AndroidRuntime: java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.beni.contactbrowser1/com.example.beni.contactbrowser1.MainActivity}: java.lang.NullPointerException 
01-15 12:59:09.007 7447-7447/com.example.beni.contactbrowser1 E/AndroidRuntime:  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1658) 
01-15 12:59:09.007 7447-7447/com.example.beni.contactbrowser1 E/AndroidRuntime:  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1760) 
01-15 12:59:09.007 7447-7447/com.example.beni.contactbrowser1 E/AndroidRuntime:  at android.app.ActivityThread.access$1500(ActivityThread.java:156) 
01-15 12:59:09.007 7447-7447/com.example.beni.contactbrowser1 E/AndroidRuntime:  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1000) 
01-15 12:59:09.007 7447-7447/com.example.beni.contactbrowser1 E/AndroidRuntime:  at android.os.Handler.dispatchMessage(Handler.java:130) 
01-15 12:59:09.007 7447-7447/com.example.beni.contactbrowser1 E/AndroidRuntime:  at android.os.Looper.loop(SourceFile:351) 
01-15 12:59:09.007 7447-7447/com.example.beni.contactbrowser1 E/AndroidRuntime:  at android.app.ActivityThread.main(ActivityThread.java:3827) 
01-15 12:59:09.007 7447-7447/com.example.beni.contactbrowser1 E/AndroidRuntime:  at java.lang.reflect.Method.invokeNative(Native Method) 
01-15 12:59:09.007 7447-7447/com.example.beni.contactbrowser1 E/AndroidRuntime:  at java.lang.reflect.Method.invoke(Method.java:538) 
01-15 12:59:09.007 7447-7447/com.example.beni.contactbrowser1 E/AndroidRuntime:  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:969) 
01-15 12:59:09.007 7447-7447/com.example.beni.contactbrowser1 E/AndroidRuntime:  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:727) 
01-15 12:59:09.007 7447-7447/com.example.beni.contactbrowser1 E/AndroidRuntime:  at dalvik.system.NativeStart.main(Native Method) 
01-15 12:59:09.007 7447-7447/com.example.beni.contactbrowser1 E/AndroidRuntime: Caused by: java.lang.NullPointerException 
01-15 12:59:09.007 7447-7447/com.example.beni.contactbrowser1 E/AndroidRuntime:  at android.app.Activity.findViewById(Activity.java:1683) 
01-15 12:59:09.007 7447-7447/com.example.beni.contactbrowser1 E/AndroidRuntime:  at com.example.beni.contactbrowser1.MainActivity.<init>(MainActivity.java:19) 
01-15 12:59:09.007 7447-7447/com.example.beni.contactbrowser1 E/AndroidRuntime:  at java.lang.Class.newInstanceImpl(Native Method) 
01-15 12:59:09.007 7447-7447/com.example.beni.contactbrowser1 E/AndroidRuntime:  at java.lang.Class.newInstance(Class.java:1440) 
01-15 12:59:09.007 7447-7447/com.example.beni.contactbrowser1 E/AndroidRuntime:  at android.app.Instrumentation.newActivity(Instrumentation.java:1056) 
01-15 12:59:09.007 7447-7447/com.example.beni.contactbrowser1 E/AndroidRuntime:  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1650) 
01-15 12:59:09.007 7447-7447/com.example.beni.contactbrowser1 E/AndroidRuntime:  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1760)  
01-15 12:59:09.007 7447-7447/com.example.beni.contactbrowser1 E/AndroidRuntime:  at android.app.ActivityThread.access$1500(ActivityThread.java:156)  
01-15 12:59:09.007 7447-7447/com.example.beni.contactbrowser1 E/AndroidRuntime:  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1000)  
01-15 12:59:09.007 7447-7447/com.example.beni.contactbrowser1 E/AndroidRuntime:  at android.os.Handler.dispatchMessage(Handler.java:130)  
01-15 12:59:09.007 7447-7447/com.example.beni.contactbrowser1 E/AndroidRuntime:  at android.os.Looper.loop(SourceFile:351)  
01-15 12:59:09.007 7447-7447/com.example.beni.contactbrowser1 E/AndroidRuntime:  at android.app.ActivityThread.main(ActivityThread.java:3827)  
01-15 12:59:09.007 7447-7447/com.example.beni.contactbrowser1 E/AndroidRuntime:  at java.lang.reflect.Method.invokeNative(Native Method)  
01-15 12:59:09.007 7447-7447/com.example.beni.contactbrowser1 E/AndroidRuntime:  at java.lang.reflect.Method.invoke(Method.java:538)  
01-15 12:59:09.007 7447-7447/com.example.beni.contactbrowser1 E/AndroidRuntime:  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:969)  
01-15 12:59:09.007 7447-7447/com.example.beni.contactbrowser1 E/AndroidRuntime:  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:727)  
01-15 12:59:09.007 7447-7447/com.example.beni.contactbrowser1 E/AndroidRuntime:  at dalvik.system.NativeStart.main(Native Method)  
01-15 12:59:09.009 258-263/? D/Settings/Provide: lookupValue, table secure cache.containsKey dropbox:data_app_crash 
01-15 12:59:09.011 258-263/? D/Settings/Provide: lookupValue, table secure cache.containsKey send_action_app_error 
01-15 12:59:09.011 258-263/? W/ActivityManager: Force finishing activity com.example.beni.contactbrowser1/.MainActivity 

AndroidManifest:

<manifest xmlns:android="http://schemas.android.com/apk/res/android" 
    package="com.example.beni.contactbrowser1" > 
    <uses-permission android:name="android.permission.READ_PROFILE"></uses-permission> 
    <uses-permission android:name="android.permission.GET_TASKS"></uses-permission> 
    <uses-permission android:name="android.permission.READ_PHONE_STATE"></uses-permission> 

    <application 
     android:allowBackup="true" 
     android:icon="@mipmap/ic_launcher" 
     android:label="@string/app_name" 
     android:supportsRtl="true" 
     android:theme="@style/AppTheme" > 
     <activity 
      android:name=".MainActivity" 
      android:label="@string/app_name" 
      android:theme="@style/AppTheme.NoActionBar" > 
      <intent-filter> 
       <action android:name="android.intent.action.MAIN" /> 

       <category android:name="android.intent.category.LAUNCHER" /> 
      </intent-filter> 
     </activity> 
    </application> 

</manifest> 

Answer 1

Instantiate ваш TextView внутри onCreate метода.

Изменение TextView tv = (TextView) findViewById(R.id.textView); только TextView tv;

И добавьте следующую строку в методе onCreate после setContentView(R.layout.activity_main); линии:

tv = (TextView) findViewById(R.id.textView);